172 PHOLADID^E. 



I now come to the most decided difference between the 

 two animals ; the foot, in the form we are now describing, 

 is proportionally larger than in any other of the Pholades, 

 of hyaline texture, springing from the centre of the body 

 with a long cylindrical pedicle; it has a subclavate appear- 

 ance, truncate at the terminus, which is of suboval form and 

 pointed anteally and posteally, and there is no outward visible 

 trace of the curious elastic stylet common to all bivalves, and 

 so conspicuous in the ventral tissue of the form Pholadidea 

 papy racea. 



I will now make a short comparison of the two forms : it 

 will be observed that it is stated, in the form Pholadidea 

 papyracea, that the mantle is closed, except a very small 

 aperture or " spiracle " for the foot, if it still exists ; but in 

 the form Pholas lamellata there is a large aperture for a foot, 

 that is, larger in proportion than in any of the Pholades. 

 The branchiae, palpi, and elaborate siphonal apparatus are 

 precisely the same, with only variations of colour ; the bodies 

 of the two are of the same shape, but differ in colour and 

 markings, the one being intensely mottled, the other hyaline ; 

 the body of the one having no foot attached to it, but the 

 other a very large one. These are the principal variations, 

 and certainly constitute a very general difference of aspect 

 between the animals of the two forms, and it must be admitted 

 that conchologists and even malacologists, who have not 

 examined with care all the conditions and incidents attached 

 to them, have had a primd facie case for doubting their 

 identity ; but notwithstanding these great and visible discre- 

 pancies, I think I shall make out a case of identity. 



In the course of my examinations I was startled by the 

 great variations in the organs of the tAvo forms of this Pholas, 

 which, twenty years ago, when I first examined this species, 

 appear not to have so rigorously excited my notice ; doubts 

 arose in my mind, that I might be wrong in my former 

 determinations of identity, and I wrote to Dr. Battersby to 

 express them to him and Mrs. Griffith, both of Torquay ; the 

 latter a lady naturalist, who has taken great interest in this 

 question; but in the summer of 1849, after a continued in- 



